One obvious problem is that accept. You don't need to accept, as the connection (between client and server) has been created already, at the time when you call ->new().

On the client side, the porgram above, you can use $t_socket for both write and read, to "listen for response", all what you need to do is <$t_socket>. Of course , for better control, you can always use select, which is something you want to learn next step.

Is there a way to tell if there is an incoming message without having to go into a while(<$t_socket>){...} loop?

(something like an if(<$t_socket>) or perhaps a function I can call on the $t_socket itself?

Thanks!

IO::Select is what you want.

The following code can show you some basic ideas of IO::Select. Follow those steps:

1. Run perl -w server.pl 3000 1
2. Run perl -w server.pl 3001 10
3. Run perl -w client.pl

Observe the client, see how it receives from server 1 (the faster guy), without being locked by the slower guy (server 2).

server

use strict;
use warnings;

use IO::Socket::INET;

my $server = IO::Socket::INET->new(Proto => "tcp", LocalAddr => "local
+host", LocalPort => $ARGV[0], Listen => 10);
my $connection = $server->accept();
print "Connected\n";
while (1) {
    print $connection "$ARGV[0]\r\n";
    print "sent $ARGV[0]\n";
    sleep($ARGV[1]);
}
[download]

client

use strict;
use warnings;

use IO::Socket::INET;
use IO::Select;

my $connection1 = IO::Socket::INET->new(PeerAddr => "localhost", PeerP
+ort => 3000, Proto => "tcp");
my $connection2 = IO::Socket::INET->new(PeerAddr => "localhost", PeerP
+ort => 3001, Proto => "tcp");

my $selector = IO::Select->new();
$selector->add($connection1);
$selector->add($connection2);

while (1) {
    my @readers = $selector->can_read(0);
    for my $reader (@readers) {
        my $line = <$reader>;
        print $line;
    }
}
[download]

I still can't seem to get the following section of code to work - it never enters the while<$t_socket>{...} loop to receive input from the Third process (the one it sends $name)

if($name eq $match)
        {
            print "Second found match: $name\n";
            print "Second sending \"$name\" to Third\n";
            
            print $t_socket "$name\n";
        
            while(<$t_socket>)
            {
                #print "Second has accepted socket to Third...\n";
                
                my $name = $_;
                chomp($name);
                
                my $t_host = gethostbyaddr($t_socket->peeraddr, AF_INE
+T);
                my $t_port = $t_socket->peerport;
                
                print "Received from [$f_host $f_port]: $name\n";     
            }
}
[download]

Do I need to do anything in particular to "listen" on the <$t_socket>?

For your reference, here is the entire code:

use IO::Socket;
use strict;
use warnings;

our $F_PORT = shift or die "Please specify First port number\n";
our $T_PORT = shift or die "Please specify Third port number\n";

#our $file = shift or die "Please specify input file\n";;

my $f_socket = IO::Socket::INET->new('LocalPort' => $F_PORT,
                       'Proto' => 'tcp',
                       'Listen' => 2)
    or die "Second: Can't create socket to First($!)\n";
   
my $t_socket = IO::Socket::INET->new( 'PeerAddr' => "localhost",
                    'PeerPort' => $T_PORT,
                       'Proto' => 'tcp')
    or die "Second: Can't create socket to Third($!)\n";

my $match = "brenna";
    
print "Second listening\n";
while(my $first = $f_socket->accept()) 
{
    #setup acknowledgement
    print "Second: Accepted connection from First..\n";
    my $f_host = gethostbyaddr($first->peeraddr, AF_INET);
    my $f_port = $first->peerport;
    
    while (<$first>) 
    {
        my $name = $_;
        chomp($name);
        
        #send acknowledgement message to First
        print "Received from [$f_host $f_port]: $name\n";
        #print $f_socket "$.: $name\n";
        
        if($name eq $match)
        {
            print "Second found match: $name\n";
            print "Second sending \"$name\" to Third\n";
            
            print $t_socket "$match\n";
        
            while(<$t_socket>)
            {
                #print "Second has accepted socket to Third...\n";
                
                my $name = $_;
                chomp($name);
                
                my $t_host = gethostbyaddr($t_socket->peeraddr, AF_INE
+T);
                my $t_port = $t_socket->peerport;
                
                print "Received from [$f_host $f_port]: $name\n";     
            }
        }                    
    }
}
die "Second: Can't accept socket from First($!)\n";
[download]

Any help would be much much appreciated... I've been beating my head against this for days now.